std::ranges::copy_n, std::ranges::copy_n_result

 

C++

Compiler support

Freestanding and hosted

Language

Standard library

Standard library headers

Named requirements

Feature test macros (C++20)

Language support library

Concepts library (C++20)

Metaprogramming library (C++11)

Diagnostics library

General utilities library

Strings library

Containers library

Iterators library

Ranges library (C++20)

Algorithms library

Numerics library

Localizations library

Input/output library

Filesystem library (C++17)

Regular expressions library (C++11)

Concurrency support library (C++11)

Technical specifications

Symbols index

External libraries

 

Algorithm library

Constrained algorithms and algorithms on ranges (C++20)
Constrained algorithms, e.g. ranges::copy, ranges::sort, ...
Execution policies (C++17)
is_execution_policy (C++17)	execution::seqexecution::parexecution::par_unseqexecution::unseq (C++17)(C++17)(C++17)(C++20)	execution::sequenced_policyexecution::parallel_policyexecution::parallel_unsequenced_policyexecution::parallel_unsequenced (C++17)(C++17)(C++17)(C++20)
Non-modifying sequence operations
all_ofany_ofnone_of (C++11)(C++11)(C++11) for_each for_each_n (C++17)	countcount_if mismatch equal adjacent_find	search search_n lexicographical_compare lexicographical_compare_three_way (C++20)	findfind_iffind_if_not (C++11) find_end find_first_of
Modifying sequence operations
copycopy_if (C++11) copy_n (C++11) copy_backward move (C++11) move_backward (C++11) shift_leftshift_right (C++20)(C++20) transform	fill fill_n generate generate_n swap iter_swap swap_ranges sample (C++17)	removeremove_if replacereplace_if reverse rotate unique random_shuffle (until C++17)	remove_copyremove_copy_if replace_copyreplace_copy_if reverse_copy rotate_copy unique_copy shuffle (C++11)
Partitioning operations
is_partitioned (C++11) partition_point (C++11)	partition partition_copy (C++11)	stable_partition
Sorting operations
is_sorted (C++11) is_sorted_until (C++11)	sort stable_sort	partial_sort partial_sort_copy	nth_element
Binary search operations
lower_bound	upper_bound	binary_search	equal_range
Set operations (on sorted ranges)
merge inplace_merge	set_difference set_intersection	set_symmetric_difference set_union	includes
Heap operations
is_heap (C++11) is_heap_until (C++11)	make_heap sort_heap	push_heap pop_heap
Minimum/maximum operations
max max_element	min min_element	minmax (C++11) minmax_element (C++11)	clamp (C++17)
Permutations
is_permutation (C++11)	next_permutation	prev_permutation
Numeric operations
iota (C++11) inner_product adjacent_difference	accumulate reduce (C++17) transform_reduce (C++17)	transform_inclusive_scan (C++17) transform_exclusive_scan (C++17)	partial_sum inclusive_scan (C++17) exclusive_scan (C++17)
Operations on uninitialized storage
uninitialized_copy uninitialized_move (C++17) uninitialized_fill	uninitialized_copy_n (C++11) uninitialized_move_n (C++17) uninitialized_fill_n	uninitialized_default_construct (C++17) uninitialized_value_construct (C++17) uninitialized_default_construct_n (C++17) uninitialized_value_construct_n (C++17)	destroy (C++17) destroy_n (C++17) destroy_at (C++17) construct_at (C++20)
C library
qsort	bsearch

 

Constrained algorithms

Non-modifying sequence operations
ranges::all_ofranges::any_ofranges::none_of ranges::for_each ranges::for_each_n ranges::lexicographical_compare      ranges::adjacent_find	ranges::countranges::count_if ranges::mismatch ranges::equal ranges::containsranges::contains_subrange (C++23)(C++23)	ranges::findranges::find_ifranges::find_if_not ranges::find_lastranges::find_last_ifranges::find_last_if_not (C++23)(C++23)(C++23)	ranges::find_end ranges::find_first_of ranges::search ranges::search_n ranges::starts_with (C++23) ranges::ends_with (C++23)
Modifying sequence operations
ranges::copyranges::copy_if ranges::copy_n ranges::copy_backward ranges::move ranges::move_backward ranges::shift_leftranges::shift_right (C++23)(C++23)   ranges::transform	ranges::fill ranges::fill_n ranges::generate ranges::generate_n ranges::swap_ranges ranges::shuffle ranges::sample	ranges::removeranges::remove_if ranges::replaceranges::replace_if ranges::reverse ranges::rotate ranges::unique	ranges::remove_copyranges::remove_copy_if ranges::replace_copyranges::replace_copy_if ranges::reverse_copy ranges::rotate_copy ranges::unique_copy
Partitioning operations
ranges::is_partitioned ranges::partition_point	ranges::partition ranges::partition_copy	ranges::stable_partition
Sorting operations
ranges::is_sorted ranges::is_sorted_until	ranges::sort ranges::stable_sort	ranges::partial_sort ranges::partial_sort_copy	ranges::nth_element
Binary search operations (on sorted ranges)
ranges::lower_bound	ranges::upper_bound	ranges::binary_search	ranges::equal_range
Set operations (on sorted ranges)
ranges::merge ranges::inplace_merge	ranges::set_difference ranges::set_intersection	ranges::set_symmetric_difference    ranges::set_union	ranges::includes
Heap operations
ranges::is_heap ranges::is_heap_until	ranges::make_heap ranges::sort_heap	ranges::push_heap ranges::pop_heap
Minimum/maximum operations
ranges::max ranges::max_element	ranges::min ranges::min_element	ranges::minmax ranges::minmax_element	ranges::clamp
Permutation operations
ranges::is_permutation	ranges::next_permutation	ranges::prev_permutation
Numeric operations
ranges::iota (C++23)
Fold operations
ranges::fold_left (C++23) ranges::fold_left_first (C++23)	ranges::fold_right (C++23) ranges::fold_right_last (C++23)	ranges::fold_left_with_iter (C++23) ranges::fold_left_first_with_iter (C++23)
Operations on uninitialized storage
ranges::construct_at ranges::destroy ranges::destroy_n ranges::destroy_at	ranges::uninitialized_copy    ranges::uninitialized_move ranges::uninitialized_fill	ranges::uninitialized_copy_n    ranges::uninitialized_move_n ranges::uninitialized_fill_n	ranges::uninitialized_default_construct ranges::uninitialized_default_construct_n    ranges::uninitialized_value_construct ranges::uninitialized_value_construct_n
Return types
ranges::in_fun_result ranges::in_in_result ranges::in_found_result	ranges::in_out_result ranges::in_in_out_result	ranges::in_out_out_result ranges::min_max_result	ranges::out_value_result (C++23) ranges::in_value_result (C++23)

 

Defined in header <algorithm>
Call signature
template< std::input_iterator I, std::weakly_incrementable O > requires std::indirectly_copyable<I, O> constexpr copy_n_result<I, O>     copy_n( I first, std::iter_difference_t<I> n, O result );	(1)	(since C++20)
Helper type
template< class I, class O > using copy_n_result = ranges::in_out_result<I, O>;	(2)	(since C++20)

1) Copies exactly n values from the range beginning at first to the range beginning at result by performing *(result + i) = *(first + i) for each integer in [​0​, n). The behavior is undefined if result is within the range [first, first + n) (ranges::copy_backward might be used instead in this case).

The function-like entities described on this page are niebloids, that is:

• Explicit template argument lists cannot be specified when calling any of them.
• None of them are visible to argument-dependent lookup.
• When any of them are found by normal unqualified lookup as the name to the left of the function-call operator, argument-dependent lookup is inhibited.

In practice, they may be implemented as function objects, or with special compiler extensions.

Parameters

first	-	the beginning of the range of elements to copy from
n	-	number of the elements to copy
result	-	the beginning of the destination range

Return value

ranges::copy_n_result{first + n, result + n} or more formally, a value of type ranges::in_out_result that contains an std::input_iterator iterator equals to ranges::next(first, n) and a std::weakly_incrementable iterator equals to ranges::next(result, n).

Complexity

Exactly n assignments.

Notes

In practice, implementations of std::ranges::copy_n may avoid multiple assignments and use bulk copy functions such as std::memmove if the value type is TriviallyCopyable and the iterator types satisfy contiguous_iterator. Alternatively, such copy acceleration can be injected during an optimization phase of a compiler.

When copying overlapping ranges, std::ranges::copy_n is appropriate when copying to the left (beginning of the destination range is outside the source range) while std::ranges::copy_backward is appropriate when copying to the right (end of the destination range is outside the source range).

Possible implementation

struct copy_n_fn { template<std::input_iterator I, std::weakly_incrementable O> requires std::indirectly_copyable<I, O> constexpr ranges::copy_n_result<I, O> operator()(I first, std::iter_difference_t<I> n, O result) const { for (std::iter_difference_t<I> i {}; i != n; ++i, ++first, ++result) *result = *first; return {std::move(first), std::move(result)}; } };   inline constexpr copy_n_fn copy_n {};

Example

Run this code

#include <algorithm>
#include <iomanip>
#include <iostream>
#include <iterator>
#include <string>
#include <string_view>
 
int main()
{
    const std::string_view in {"ABCDEFGH"};
    std::string out;
 
    std::ranges::copy_n(in.begin(), 4, std::back_inserter(out));
    std::cout << std::quoted(out) << '\n';
 
    out = "abcdefgh";
    const auto res = std::ranges::copy_n(in.begin(), 5, out.begin());
    std::cout
        << "*(res.in): '" << *(res.in) << "', distance: "
        << std::distance(std::begin(in), res.in) << '\n'
        << "*(res.out): '" << *(res.out) << "', distance: "
        << std::distance(std::begin(out), res.out) << '\n';
}

Output:

"ABCD"
*(res.in): 'F', distance: 5
*(res.out): 'f', distance: 5

See also

ranges::copyranges::copy_if (C++20)(C++20)	copies a range of elements to a new location (niebloid)
ranges::copy_backward (C++20)	copies a range of elements in backwards order (niebloid)
ranges::remove_copyranges::remove_copy_if (C++20)(C++20)	copies a range of elements omitting those that satisfy specific criteria (niebloid)
ranges::replace_copyranges::replace_copy_if (C++20)(C++20)	copies a range, replacing elements satisfying specific criteria with another value (niebloid)
ranges::reverse_copy (C++20)	creates a copy of a range that is reversed (niebloid)
ranges::rotate_copy (C++20)	copies and rotate a range of elements (niebloid)
ranges::unique_copy (C++20)	creates a copy of some range of elements that contains no consecutive duplicates (niebloid)
ranges::move (C++20)	moves a range of elements to a new location (niebloid)
ranges::move_backward (C++20)	moves a range of elements to a new location in backwards order (niebloid)
copy_n (C++11)	copies a number of elements to a new location (function template)